1. Field of the Invention
The present invention relates to a transmission for a working vehicle that is designed to transmit drive power from an engine to a driving axle. The present invention also relates to a vehicle with a power transmission train designed to transmit drive power from an engine to a driving axle via a main-speed-change unit and a sub-speed-change unit.
2. Related Art
A vehicle such as a working vehicle has a power transmission train, which is designed to transmit drive power from an engine to a driving axle via a speed change unit, enabling the driving axle to be rotated at a predetermined speed by the operation of the speed change unit. If a need exists to widen a speed change range of the driving axle, and/or reduce the load applied to the speed change unit, a sub-speed-change unit is further provided in addition to a main-speed-change unit.
FIG. 22 is a model view of a conventional vehicle equipped with a main-speed-change unit and a sub-speed-change unit, in which a rear axle serves as a driving axle. As illustrated in this Figure, the conventional vehicle equipped with the sub-speed-change unit has engine 801, flywheel 802, main-speed-change unit 803, sub-speed-change unit 804 and driving axle unit 805, which are detachable from each other, aligned in sequence from one side of a vehicle to the opposite side thereof in the longitudinal direction and connected in tandem. This particular arrangement may cause the following problems.
That is, when a hydrostatic transmission (hereinafter referred to as HST) is used as the main-speed-change unit 803, the HST itself vibrates due to pulsation or the like of operating fluid pressure circulating in the HST. As mentioned above, the arrangement with the main-speed-change unit 803, the sub-speed-change unit 804 and the axle unit 805 connected to each other cause vibrations of the HST to be transmitted to vehicle frame 800 via the sub-speed-change unit 804 and the axle unit 805, thereby causing the problem of deteriorating a driving conditions.
In order to solve the above problem, there was proposed an arrangement wherein the engine is connected with the sub-speed-change unit through a housing, and the HST, serving as the main-speed-change unit, is connected with the front side of the sub-speed-change unit via an antivibration members. The front side of the HST is then connected with the housing via another antivibration member.
However, in the above arrangement, there is no consideration made for vibration of the engine. That is, the above power transmission arrangement causes a problem wherein the housing itself, which supports the HST with a flexible structure omitting transmission of vibrations, vibrates due to vibrations transmitted from the engine.
In the above arrangement, the engine, the housing and the sub-speed-change unit are connected in tandem, with the result that a space does not exist between front and rear wheels. Accordingly, a driver's step must be disposed above those members connected together, which necessitates the driver's step to be disposed at a higher place, and/or those connected members to be disposed at a higher place in a case where a mid-mount mower must be mounted between the front and rear wheels, hence inviting rise of the vehicle's center of gravity.
The present invention has been conceived in consideration of those prior arts. It is an object of the present invention to provide a transmission for a working vehicle with a power transmission train designed to transmit drive power from an engine to a driving axle via a main-speed-change unit and a sub-speed-change unit, which is capable of effectively preventing vibrations due to the engine and the main-speed-change unit from transmitting to the vehicle frame.
It is another object of the present invention to provide a transmission for a working vehicle that is capable of securing a free space between the front and rear wheels without inviting expansion of the vehicle's length.
It is still another object of the present invention to provide a vehicle with a power transmission train designed to transmit drive power from an engine to a driving axle via a main-speed-change unit and a sub-speed-change unit, which is capable of effectively preventing expansion of the vehicle's length, as well as securing a free space between the front and rear wheels.